Some position detection systems related to touch screens sense the interruption of radiation (e.g., light) by an opaque object (e.g., a finger, stylus, etc.). Such systems generally utilize radiation transmitters for transmitting radiation across the field of the touch screen, parallel to the viewing field surface. Radiation receivers are used to detect the radiation that passes across the field of the touch screen and sense the existence and location of any interruption in this radiation by the opaque object.
A retroreflective sheeting material may be positioned around the perimeter of the active field of the touch screen, as disclosed in U.S. Pat. No. 4,507,557. The retroreflective sheeting material is generally arranged to reflect radiation received from an originating source back toward the originating source. An exemplary retroreflective sheeting material generally includes a layer of clear resin, such as acrylic, polycarbonate or vinyl, having a smooth front surface and a plurality of retroreflective cube corner prisms on the reverse surface. Light incident on the smooth front surface passes through the sheeting, impinges on the retroreflective elements, and is reflected back out through the smooth front surface in a direction nominally 180 degrees to the direction of incidence.
One problem with the use of certain conventional retroreflective sheeting materials in touch screen applications and/or position detection systems is that dirt and/or moisture may penetrate the structure and adversely affect retro reflectivity of the retroreflective sheeting material. Another problem with conventional retroreflective sheeting material used in touch screen applications and/or position detection systems is difficulty in obtaining a uniform background throughout the area of interest (e.g., the detection area), against which the opaque object can be contrasted. Many conventional retroreflective sheeting material designs provide a non-uniform background and have portions, especially at or near the corner regions where the detected signal is very low. This makes it difficult to detect movement of the opaque object in such areas.